1. Field of the Invention
The present disclosure relates to a liquid crystal display device including a back light unit. Specifically, the present disclosure relates to a back light unit having an LED array structure for reducing light leakage problem at edge portion.
2. Discussion of the Related Art
An active matrix type liquid crystal display device (or “AMLCD”) represents video data using a thin film transistor (or “TFT”) as the switching element. As the AMLCD can be made in a thin flat panel with light weight, it is replacing the cathode ray tube (or “CRT”) in the display device market and is being applied to portable information appliances, computer devices, office automation appliances, and/or television sets.
The AMLCD comprises a liquid crystal display panel (or LCD panel), a back light unit for irradiating light to the LCD panel, a light source driving circuit for controlling the light source of the back light unit, a data driving circuit for supplying the data signals to the data lines of the LCD panel, a gate driving circuit for sequentially supplying the gate pulse (or scan pulse) to the gate lines of the LCD panel, and a timing controller for controlling the operating timing of the data driving circuit and the gate driving circuit. Recently, the light emitting diode (or LED) is being applied to the back light unit as the light source. As the temperature increases, the efficiency and the service lift time of the LED will be degraded. To solve these drawbacks, a metallic printed circuit board having advanced qualities for radiating the heat from the light source is being used for mounting the LED packages.
There are two types of LED arrays, depending to the method used for forming the LED package. One is the white LED array type in which multiple white LEDs are arrayed. The white LED array type is made by mixing the material having a yellow color material to the LED radiating a blue color. Therefore, according the color brightness distribution graph of the white LED, the white LED array type does not have even brightness distribution over RGB color bands. FIG. 1 is the graph illustrating the color brightness distribution according to the color wavelengths of the white LED array type. The other is the RGB LED array type in which red (R) LED, green (G) LED and blue (B) LED are sequentially arrayed for making a white color by mixing RGB colors. The RGB LED array type has the advantage of having back light with even color brightness distribution over all wavelengths covering R-G-B color. FIG. 2 is a graph illustrating the color brightness distribution according to the color wavelengths of the RGB LED array type. However, in the RGB LED array type, there is another problem in which color of the last arrayed LED is more brightly represented at the edge portion of the LCD panel.
For example, LED back light source may be positioned at the left side of the LCD device, and the LED back light source may has R, G and B LEDs sequentially arrayed from the lowest point of the left side. In this case, at the lowest point where the red (R) LED is disposted, the red color can be more brightly shown. This is called the redish problem. FIG. 3a is the picture illustrating the redish problem occurred at the edge type LED back light unit. FIG. 3b is the picture illustrating the redish problem occurred at the direct type LED back light unit. This redish problem is caused by that the red light from the end red LED is radiated without properly mixing with the other lights from other LEDs. To solve this problem, there is one method in which the brightness of the lastly positioned LED is lowered. However, this method may cause other problems such as the complexity problems of the circuit implementation and the manufacturing method, and high cost problems.